Preparation of pure copper metal from copper-bearing scrap



Aug- 4, 1953 L. N. ALLEN, JR., ET Al. 2,647,830

PREPARATION OF' PURE COPPER METAL f FROM COPPER-BEARING SCRAP Filed Dec. 17, 1949 BY @uw ATTORNEY Patented Aug. 4, 1953 PREPARATION OF PURE COPPER METAL FROM COPPER-BEARIN G SCRAP Louis N. Allen, J r.,- Short Hills, N. J., and Patrick J. McGauley, Glen Cove, and Edward S. Roberts, New York, N. Y., assignors to Chemical Construction Corporation, New York, N. Y., a.

corporation of Delaware l Application December 17, 1949, Serial No. 133,666

` (o1. 75-1os) 16 Claims. 1

The present invention relates to :the recovery of copper from copper-bearing scrap metal. In particular, it relates to an improved method whereby the copper content of such materials is quickly, simply and easily leached and subsequently recovered.

In recent years .the metalsl trades have :been faced with a constantly increasing demand for non-ferrousY metals, particularly copper. This has been accompanied by a decrease in the known reserves Vof high-grade ore and rapidly increasing costsy of miningand refining the lower grades. As a result, more and more interest is being displayed in methods for recovering the copper con-` tent of copper-bearing scrap metal.

What is probably the best current practice in the field is readily illustrated. Copper-bearing scrap is charged into large leachingvvats and flooded with a diluteoxidized rsolution of ammoniacal copper'carbonate.` `The latter solution is gently circulated through the layer, pumped through lan oxidation tower andreturned to the leaching tanks. In this manner the copper in solution is alternately oxidized to cupric salts and then returned tothe cuprous condition in dissolving more copper.` New barren solution is constantly added to the system and the pregnant solution is continuously withdrawn.

As a result, not only copper butzinc and other soluble impurities are gradually dissolved into a collective. relatively dilute solution. The ratefof dissolving of the various metals -is not the same for each. Copper and zinc will dissolve at approximately the same rate,- whereas nickel will dissolve at a somewhat slower rate. Lead will dissolve up toa lcertain saturation andremain constant. The ammonium carbonate and ammonia are then distilled. off and ,the copper recovered, principally, as impure cuprous oxide. Mother liquor from the system is discarded while the Jammonia and carbon dioxide vapors are condensed in watenbeing reused in the leaching of more scrap.

. `It will be seen thatv this ,process is `extremelyslow. Leaching of normal copperl scrap with these dilute solutions requires that the scrap remain in the leaching tanks for a period ofat least three to six weeks.. -This unreasonably long leaching period requires `such a large and expensive inventory of both metal andrammonia in process that the carrying charges become an important item in the total cost of processing. The long leachingperiod requires anexcessive number of leaching tanks, as well as amount of solution and equipment.- Therelatively dilute leachpurities in the copper oxide product from the` Still.

Copper oxides precipitated in the still tend to.

build up on the inside of the vessel and must be periodically removed by hand labor. The high steam requirements of the still are an important part of the cost of the process. The resulting impure copper product must be reduced and refined before it is marketable as commercial copper metal. Lead and zinc impurities are distilled off during the reducing and rening operation. Nickel, however, remains in the copper and to remove it requires an expensive separation process. i Therefore, the presence of nickel in substantial quantities, markedly reduces the utility of the resulting impure oxide. Nevertheless, the economy of still operation makes the useof dilute leaching solutions desirable.

It would seem fairly simple. to increase the leaching rate. For example, it would appear to be more desirable to increase theconcentration of the leaching liquor. However, if this is done, the economy of still operation is radically altered. It `becomes such as to offset any economic gain in the shorter time required for leaching.

,x There remains, therefore, a commercial demand for a process, the utilization of which is not hampered by these drawbacks. It is, accordingly, the principal object of the present inventionv to devise a method which is faster, easier and more effective. Preferably it should involve the the use of no unusual or expensive apparatus and should not involve` the necessity for extraordinary or expensive reagents.

In general, the overall objects ofthe present invention have been effectively accomplished by a combination of modications of the general practice. One radicalmodification comprises a marked increase in the concentration and rate of circulation of liquor over the pieces to be leached. A second lies'in la novel system for making up and recycling uid whereby the system is kept in material balance with little or no waste of effective reagents. A third lies in a novel system for reducing the copper content of the leach solution tov metallic copper and subsequently puriiying this copper to produce a product whichv is 99.9+% pure.

l.In view of the fact that in previous practice the rate of leach fluid circulation has been considered irrelevant, the first modication, as applied in the present process is particularly surprising. In the past, it has been thought necessary to circulate the leach fluid only suiiiciently to maintain its strength by passing a sufficient amount through the oxidizing tower. In accordance with the present invention, it has been found that the leaching rate is proportional, almost directly within a considerable range, to the concentration of cupric copper in the leach liquor, and is almost directly proportional to a factor which corre;- sponds to the one-third power of the velocity oi the fluid over the piece being leached.k

Accordingly, in the practice of this invention, the circulation of fluid over the leachingpieces is governed by the desired leaching rate. Flow velocities are maintained many times higher than those previously used. The velocity will ordinarily be as high as practically obtainable with the available apparatus. Increasing this. velocity. beyond a certain point, however, reaches. a point of rapidly diminishing return. Increasing the velocity increases the necessary size of the apparatus landthe pumps and other apparatus used to maintain the circulation rate. An economic balance must be taken between the improvement due to increasing the velocity and cost of maintaining such a velocity.

It has been found that a Velocity over the sur-- face of the pieces being le'ached of 0.01-5 feet per second should be used. Higher velocities may be used but pumping costs become excessive. Ordinarily, the most useful practice will range from about 0.05 to 1.0 foot per second, a good average practice being about 0.5 foot per second. Actual operation at these velocities is conducted by the'u-se of a series of tanks. The solution is recirculated within each tank to obtain the desired velocity. The gross quantity of copper being leached per unit of time within a given tank gradually diminishes as the available copper surface decreases. Accordingly, it is desirable to have a plurality of tanks operating simultaneously but each at a different stage inthe operation. In this way a substantially constant overall rate of leaching may be maintained.

Several additional factors which affect the leaching range should also be considered. The rate is increased as the temperature is increased. The temperature of operation should be as high asl practicable without .seriously reducing the solubility of the ammonia. In general practice, however, no attempt .should be made to actually increase the. temperature of the leach liquor beyond the eiiluent. temperature from the oxidation tower. The latter usually will be 100-135' F. Precautions sho'uld be taken to avoid loss of heat in the oxidation and leaching systems to preserve as high reaction rates as possible.

As noted above, leaching rate is also 'aected' by the amount of cupri'c copper available in the leaching liquor. This may be varied considerably. 'Inthe past, as also noted abo-ve, it has been'considered economically necessary that the leaching 'solution be quite dilute. In accordance with the present invention, this is not found necessary. This is due to the fact thatl the economy-of the still operation in the previous practice favored dilute leaching solutions.

In the present invention,r as will be broughtV out below, this is not a serious factor, dueto the novel liquor treating `and recirculation systems. The strength of the leach liquor may be kept as high asconveniently practicable. However, copper, copper salts or other impurities should not be precipitated in thek system at any point except in the reduction vessels where metallic copper is precipitated. Accordingly, it has been. found preferable to use a leach liquor initially containing at least 20 but not more than about 100-110 grams of cupric copper per liter. This may go as high as about 175 grams during operation. In general .practice this range willv be reduced somewhat when appreciably .large quantities of zinc are being leached out along with the copper v in the leach tanks.

with 'which this application is primarily concerned, .have Vbeen discussed. The remainder of the procedure may be carried out in any desired manner. vFor the purpose of illustration, a novel operational procedure which may be considered as constituting a series ofseparate but interlocking steps hasl been set forth below.

Initially, 'typical operations will be described below withreference tothe treatment of copper scrap which ises-sentlally 'free from large amount of impurities, usually or better in copper. Necessary deviations from this .system .caused by the dissolution of and the necessity for the removal therefrom of dissolved'metalsother than copper, willbe then discussed.

Initially the spentleach vliquor is divided into two ilows. One flow, which :will be considered later, is returned 'for oxidation. Theremaining portion is treated to recover/the precipitatable copper content. It is this latter 'operation which next will be considered.

It is believedfthat'the discussion of the invention may be more readily'followed in conjunction with the accompanying drawing which is a simplified flow scheme showing the essential features of the process.

This portion of `the liquor, i. e.,:that from which copper isto be recovered, is to be reduced with carbon monoxide-is pumped against'pressure into -an absorption tower in which itis-saturated, as nearly as is `practically possible, with carbon monoxide. In conducting this operation the procedural limits may also'be-varied considerably First,'to improve the absorption rate, the liquor should be cooled to about 90F. vor lower. Pressure in the absorption tower may also be varied considerably in accordance with'the possibilities of theavailable apparatus. It has been lfound that about '750 to 1250 pounds per square inch is a good practice with the average pressure of about 10001-50 -pounds being preferred. VIhis limit, however, is notcritical.

As a sourceiof carbon monoxide, many kinds of any available commercial gas may be used. Sulfur is undesirable therein. The-pressurey of carbon dioxide or nitrogen as diluents have'no adverse effect except furthe necessary increase in the volumes handled. Producer gas except for the sulfur content which may be removedif necessary is completely satisfactory and lts-use-Will be taken as illustrative. Other equivalent-and preferable sulfur-free gases include water gas,'re formed methane, andthe like. During'absorption thetemperaturewillrise-to about F. to .F. Elliuent. gases, containing nitrogen `and the unabsorbed CO and CO2, aswell` as some'ammonia, are further-.treatedfwith cold water .in a packedttowersecton, also under pressure. The ammonia will lbe dissolved in this waterandzthe resultant solution is added to the main liquid effluent.` The residual inert gases, substantially free 'from ammonia, may be vented to waste through a suitable reducing valve. They also may Ibe sent alternati-vely to some suitable power recovery unit. Under good operating conditions the gas-saturated liquor will contain cuprous copper, cupric copper, carbon monoxide and water in the correct mole ratio to precipitate about 70% of the copper content. As will be brought out, while not an essential limitation, this degree of precipitation does constitute a good average practice. Precipitation is accomplished by transferring the liquor to a suitable pressure vessel and raising its temperature, usually with steam, to above about 250 F., usually 300-350 F., for carbon monoxide vbeing good practice. The time of treatment will varyl with the temperature. Preferably, also, the pressure vessel should be equipped for mechanical stirring, which will markedly improve the rate of reaction. For example, using carbon monoxide a fteen minute treatmentat about 300 F. will constitute a good average practice. Temperatures above about 350 F. with carbon monoxide may be used if so desired; however, to do so is not necessaryand will ordinarily be found to unduly increase the apparatus requirements.

'Precipitation of copper preferably should be accomplished ina continuous fashion. Steam and pregnant liquor are continually added to the vessel and copper powdery slurry and spent liquor continually discharged. The eilluent slurry is indirectly cooled to about 150 to 175 F. and the pressure thereon reduced to atmospheric. In this range the'vaporl pressure of the liquid will be about atmospheric and this constitutes the preferred practice.

Metallic copper is separated from this slurry, then washed and dried. Preferably, thisv is done using successive Washings with ammonia-bearing liquor water, with metallic-lead-dissolving reagent, with metallic-nickel-dissolving reagent and finally with water. Wet copper metal is mechanically dried to the extent found practical, followed by complete drying in a hydrogen atmosphere and heating t about 400"v F. The product` is pure powdered copper metal containing 99.9+%

copper. i y i The decanted liquid which willV contain the residual dissolved copper is combined with the first metal wash liquor which will contain ammonia and in some cases copper and then treated to remove CO2 and H2O to the extent required to balance the incoming materials to the overall process. This may be done in any of several ways. When copper is substantially the only dissolved metal, the only case thus far discussed, this may be done by an operation that comprises an additional novel feature of the present process. It is useful in this case because the amount of residual dissolved copper will be small. In this operation, approximately one-third of this liquorl is treated to strip dissolved gases therefrom. The remanider is used in an absorption treatmentof the stripped gases.

Strippingis preferably carried out in a suitable packed tower, at about atmospheric pressure, with live steam. Evolution of CO2 and NH3 and precipitation of copper oxide results. The stripped effluent is then filtered. Thereby, the necessary water to be discarded is separated out. `The precipitated solids, including the copper oxide is returned to the system usually by redissolving, as will be more fully noted below.

The remaining portion of ,the uid, that used Substantially all `of `the NH3 is dissolved. However, according to this invention, it has been found that rates of absorptionfor CO2 and NH:

differ suliciently so that of theammoniaV can be dissolved, `while dissolving only about 10% of the carbon dioxide. The undissolved gases are treated also with cold water to pick up any remaining NH3, and an additional small portion of CO2.v However, the overall result is `the evolution of sufliciently more CO2 in the stripper than will be redissolved to deliver the necessary amount of C02 to be removed from the overall system. In many cases, the correct amount of water will be discharged from the lter to balance the cycle. yIf more water must be discharged, additional COz must be evolved in the final cold water scrubber. l However, this amount may be added back at any convenient point, for example in the oxidizing tower. Conversely, if more CO2 need be evolved, additional H2O may be discarded through the filter and the additional water may be returned at any convenient subsequent point.

Discharge from the ammonia reabsorption operation usually will be found to be at about o F. This is the uid used to redissolve the copper oxide precipitated in the stripper. As was noted above, this copper oxide now constitutes a major part of the solids in the lter sludge.

Leach liquor which is to be returned to the dissolving tanks will be a composite made up of spent leach solution and the return ammoniacopper solution obtained after the H2O-CO2 removal operation just discussed. These two liquors, usually but vnot necessarily commingled, are subjected to oxidation. Again it is desirable to operate below about 90 F. to favorably influence the absorption rates. Cooled liquors are passed through a suitable oxidizer, usually a packed tower, countercurrently to a stream of air, oxygen, or oxygen-enriched air. Some ammonia will be driven off. This is again redissolved in cold water in a separate operation and is added to the oxidized liquid eiiluent. A

While the foregoing discussion has been principally concerned with copper, not all scrap metals requiring treatment constitute pure copper. Some is copper clad steel. This presents no difficulty as the iron is unreacted by the copper ammonium carbonate solution. Other scraps may contain zinc, lead, tin or nickel, for example. Zinc, for example, will form zinc carbonate which is soluble in ammonia leach solutions. Zinc, then, will build up to some concentration determined by input and output. Where it is necessary to remove zinc and other like dissolved metals, a modification of the flow is desirable. Probably, the most convenient method of removing the zinc carbonate and the like is to divide the-flows before pure copper precipitation. A portion of leach liquor is subjected to a complete copper precipitation regardless of purity.v This" precipitate is recycled, preferably to the cupriccuprous reduction. Precipitation is done exactly as that discussed above except that it is carried tol completion. Heating should continue for'a considerably longer period of time than, and as noted, Iusually to a temperature above that nor-` mal for the step of precipitating only so much copper ascomes down pure. If Vso desired, liquor remaining after the '70% precipitation and wash water from. that fraction maybe added `to this .acomodo 7' circuit'. v Ordinarily this need not pedone." The zinc carbonate is in the remaining solution alongv with carbon dioxide and ammonia-and is thereby removed. Usually' 'a continuous ilow thru this purging side circuit ils maintained.

It has been fox-1ndby' actual practice that. the portion of thev copperwhich precipitates between 701% and 100% total' copper reduction is less pure than the copper which precipitates at or below '1,09% total copper reduction. Therefore, in this side circuit a separation will be made whereby all of the copper precipitating between (l and 100% or, alternatively', if a part of the liquor' after 79%* precipitation isadded thereto, between 79% and 100%., will be separated from the removal liquor flow and 'be turned back to the leaching' or' reduction vesselsv for redissolving.

This separation is accomplished byv first cool-- ing the-mixture or rr-ieta-lfl-icA copper and liquor and then relieving the liquor' toatmosphericpressure. Copper is filtered out or the mixture is then allowedto settle. Clear liquor containing zinc carbonate', C02 and ammonia can be'decanted. Decanted liquor' and/or nitrate is: processed in a stripping' still to recover' in asimilar mannerto that described previously. The eluent `from ths' still will contain Zinc carbonate and water. The zinc carbonate may be separated by' any con-- ventiorral 'means and the Water discarded. 1=nl this manner, a portion oralll or? the water which is required to be discarded in the process may be eliminated. The stripped gases are thentaken upih-'one of the news returningv to leaching or reduction.

Lead will partially dissolve asl leadcarbonate soluble' in ammonia. Thev balance will' form a sludge in the leaching tanks, alongl with-tin and rare metals. These-may be recovered. A portion ci the soluble lead will be reduced with thecopper s'omecases. Proportionately, however, it' precipitates muchv slower than copper, so ordi'- narily it will not all come down. Precipitated lead', if' any, may be removed by a suitable reagent. This' may' be a soluble'V ferricyanide in a slightly'l acidic solution, the acid being' selected from a group which forms soluble lead salts. It also may be removed with acetic' acid, orV a soluble;V acetate and' an' oxidizingreagent".

'Nickel will dissolve to'A some extent along' with copper and will be proportionately reduced. Like' the lead, it may be wash-ed fromy the copper. It will! be removed by a` weak' sulfuric acid wash. Since-'the latter is' ordinarily' used* to stabilize the copper;- if for no other' reason, this will' be' taken' care of: by normal operation. In the process of the present' invention', the d'lilicuity occasioned' by'nickel', cobalt and the like in the' scrap is considerably' reduced at the normal* operating temperature',fboth in' leaching and copper metalproduction. m the present process' botlr the' leaching and` the copper precipitation temperatures` are; Well' below' the optimum conditions' for these metals; Operating conditions are such' that' all' theA copper'will be l'eachedA before all the rnichel` or cobalt can' be' dissolved', except when present in very small amounts proportionately' to' the' copiper.

' We. claim:

' l. In recovering' copper' from' copperebearing material by leaching said material with an' aque'- ous almnorriacal-A copper salt solution' and chem'- i :a1'l5 precipitating copper from the' leach liquor; the improvement which' comprises preparing' an' ammoniacalcopper'salt solution initially'- contain'- ing atleast 20'; but not more than about' 110'grarn's of cupric copperA per liter, and contacting' the solution thus prepared with copper-bearing material at a velocity of'v about 0.01-50 feet per second over the surface.

A process according to claim l, in which the leach liquor is contacted the copper-bearing material at' a velocity of from about @1l-1.9- foot per second over the surface.

3. in recovering copper" metal oi high purity coppe-rehearing material by leaching sai-d material with an aqueous` ammoniacal copper sal-t solution and chemically precipitating copper from th-,ey leach liquor', the improvement whichy comprises' preparing' an ammo-niacal copper' salt solution initially-containing at least 20, but` notl more than about 11d grams of cupric copper per liter, and' contacting the solution thus prepared with copper-bearing. material at a velocity of about 0.01-5-0i'eet per second over' the surface', withdrawing sperrt leach liquor and treating' withdrawn liquor with a substantially sulphur'- free reducing' gas for a time sufficient' to' effect precipitation only' of copper powder at a purity of at least 99.9%.

4. In recovering. copper' metal' of high purity' from copper-hearing' material by' leaching' said material with. an ammoniacal copper salt' solution and chemically precipitating` copper from leach liquor,y the improvement which comprises preparing an. ammoniacal copper salt leaching solution containing from aboutV 2G to. about. ll'O grams of, cupric copperv per liter, contacting solution thus prepared with said material at, a velocity of. about (lOl-5.0- feet per. second, over the surface, whereby.7 the total dissolved. copper content of said solution is increased with an. equivalent reduction of cupric: to-cuprous coppenwhle: subjecting. withdrawn. leaching solution to suthcient oxfliawtion; to convert cuprous copper therein to Cupido, returning, oxidized liquor to' the. leaching operation and maintaining'` the; rates. of (a. how through and (1r): oxidation. in saldi oxidizing cir'- (nuit` sufficentlyf high to maintain the cupric,- cuprous rairlo in said'leaclingi solution at', an ac.- tive' leachinglevel throughout saidcontacting op'- eration.

5. In recovering copper metal of high puri-ty from copper'-bearingt material byl leaching said materialx with an ammoniacal' copper salt solutionand chemically' precipitating copper from' the lleach liquor, the improvement which' comprises contacting an ammoniaca'l copper' salt' leaching solution initially containing' from about' 2U to about' llO grams 'of' cupric copper per` liter with said material' at a velocity of about GL01- 5.0" feet per second' over thev surface, whereby the total copper content oi said solution is: increased with an` equivalentreduction. of cupric toy cuprous copperv while subjecting, withdrawn leaching. solution. to.- suicient oxidation` toy convert. cuprous copper. therein to. cupric. returning. oxidized liqucr' tovv the: leaching operation and., maintaining the rates of (a) flow through and (ha oxidation nsairi, oxidizing. .circuit suicently high to.- maintain thecupric-cuprous.` ratio iny saidL leaching solution. at. activezlcaching, lepelgz' treating, ad ditional Withdrawn: leachingc solution at. increased pressure andi abcvez about 25W-Wilma substantiailiy snlphurhfrseec reducing gas` for a time; sui-iicientteilectz partial-:precipitationot only copper powder 'off' at. least.- 99 192%.. and recycling' any' copper not so precipitated' from; the' solution', thereby' obtaining in a. series of cycliesa substan- 9 tially complete recovery of all leached copper as a metal powder of at least 99.9% purity.

6. A process according to claim in which said leaching solution is contacted with the copper-bearing material at a velocity of about 0.1-1.0 foot per second over the surface.

7. A process according to claim 5 in which the effective reducing component of said reducing gas is carbon monoxide.

8. In recovering copper metal of high purity from copper-bearing material by leaching said material with an ammoniacal copper salt leaching solution initially containing from about 20 to about 110 grams of cupric copper per liter with said material at a velocity of about 0.0l-5.0 feet per second over the surface, whereby the total copper content of said solution is increased with an equivalent reduction of cupric to cuprous copper, while subjecting Withdrawn leaching solution to suflicient oxidation to convert cuprous copper therein to cupric, returning oxidized liquor to the leaching operation and maintaining the rates of (a) flow through and (b) oxidation in said oxidizing circuit sufficiently high to maintain the cupric-cuprous ratio in said leaching solution at an active leaching level; the improvement Which comprises treating additional withdrawn leaching solution at increased pressure and above about 250 F., With a substantially sulphur-free reducing gas for a time sufficient to effect partial precipitation of only copper powder of at least 99.9% purity and recycling any copper not so precipitated from the solution, thereby obtaining in a series of cycles substantially complete recovery of all leached copper as a metal powder of at least 99.9% purity.

9. A process according to claim 8 in which at least a portion of said residual unprecipitated copper in solution after the initial precipitation of high-purity copper only is precipitated from solution before being recycled.

10. A process according to claim 8 in which after said precipitation of high purity copper, gases including ammonia are removed from at least a portion of said residual solution, thus removed ammonia is redissolved and unstripped residual solution and redissolved ammonia are recycled to the leaching operation.

11. A process according to claim 8 in which the partial precipitation of high purity copper only is effected Within a temperature range of about 250350 F. and a second copper precipitation is carried out with additional amounts of said reducing gas Within a temperature range of about 250-400 F. and at least an equivalent pressure, so-precipitated copper of less than about 99.9% purity being recycled.

12. A process according to claim 11 in which after the second precipitation of copper, gases including ammonia are removed from at least a portion of said residual solution, thus removed ammonia is redissolved and unstripped residual solution and redissolved ammonia are recycled to the leaching operation.

13. A process according to claim 8, which includes the steps of stripping gases, including ammonia, from at least a portion of the residual solution after said precipitation of high purity copper; redissolving stripped ammonia; oxidizing at least a portion of any residual unstripped solution and returning redissolved ammonia and oxidized unstripped solution to the leaching operation.

14. A process according to claim 8, which includes the steps of stripping gases, including ammonia, from at least a portion of the residual solution after said precipitation of high purity copper; redissolving stripped ammonia and returning redissolved ammonia to the leaching operation.

15. A process according to claim 14 in which, prior to said stripping step, solution to be stripped is treated at increased pressure and at above about 250 F. with additional substantially sulfur-free reducing gas for sufficient time to eiect substantially complete precipitation of copper, together with any concurrent precipitation of impurities and resulting precipitate is returned as copper-bearing material to the leaching operation.

16. A process according to claim 14 in which said stripping operation is carried out to the extent that substantially all dissolved copper and ammonia are removed from the stripped solution and copper and copper-bearing solids thus obtained are returned to the leaching operation.

LOUIS N. ALLEN, JR. PATRICK J. MCGAULEY. EDWARD S. ROBERTS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,131,986 Benedict Mar. 16, 1915 1,461,918 Laist July 17, 1923 1,516,356 Taplin Nov. 18, 1924 1,570,858 Perkins Jan. 26, 1926 1,686,391 Muller et al. Oct. 2, 1928 2,290,313 Caron July 21, 1942 

1. IN RECOVERING COPPER FROM COPPER-BEARING MATERIAL BY LEACHING SAID MATERIAL WITH AN AQUEOUS AMMONIACAL COPPER SALT SOLUTION AND CHEMICALLY PRECIPITATING COPPER FROM THE LEACH LIQUOR, THE IMPROVEMENT WHICH COMPRISES PREPARING AN AMMONIACAL COPPER SALT SOLUTION INITIALLY CONTAINING AT LEAST 20, BUT NOT MORE THAN ABOUT 110 GRAMS OF CUPRIC COPPER PER LITER, AND CONTACTING THE SOLUTION THUS PREPARED WITH COPPER-BEARING MATERIAL AT A VELOCITY OF ABOUT 0.01-5.0 FEET PER SECOND OVER THE SURFACE.
 2. A PROCESS ACCORDING TO CLAIM 1, IN WHICH THE LEACH LIQUOR IS CONTACTED WITH THE COPPER-BEARING MATERIAL AT A VELOCITY OF FROM ABOUT 0.1-1.0 FOOT PER SECOND OVER THE SURFACE. 